Methods of making a lignocellulose product and products resulting therefrom



United States Patent 3,011,9fifi Patented Dec. 5, 1961 3,011,960 METHGDS OF MAKING A LIGNOCELLULOSE PRODUCT AND PRGDUCTS RESULTING THEREFRGM William T. Glah, Dubuqne, Iowa, assignor, by mesne assignments, to Durel Incorporated, Buhuque, iowa, a corporation of Iowa No Drawing. Filed Get. 3, 1958, Ser. No. 765,043 4 Claims. (Cl. 106-163) This invention relates to methods of making a lignocellulose product and to the products resulting therefrom.

This application is a continuation-in-part of my copending application, Serial No. 443,711, filed July 15, 1954, now US. Patent No. 2,864,715.

It is an object of this invention to provide an improved method of making a moldable composition comprising reacting an essentially dry mixture including comminuted lignocellulose and a reactant including a base while confining the mixture of lignocellulose and reactant under superatmospheric pressure.

Another object of this invention is to provide such a method wherein the reaction is conducted in an atmosphere of steam at about 300-550 F. for about 4-60 minutes.

A further object of the invention is to provide lignocellulose products prepared by the above methods.

Other objects and advantages of the invention will be apparatus from the following description of several embodiments of the invention.

An important advantage of the invention appears to be the controlling of the reaction so that the alpha cellulose is reduced in molecular size sufficiently to prevent swelling of subsequently fabricated products but not to the extent that toughness of fibre is lost. This latter occurs under drastic degradation and starts to become quite serious when approximately 25% of the lignocellulose has been lost as either gaseous or soluble by-products.

Another advantage appears to be the plasticization of the lignin component during the controlled cellulose degradation so that the lignin can subsequently be made to flow and function as a binder between the comminuted lignocellulose particles.

Another advantage is the provision of a relatively dry system so that high capacity for the processing of, for example, wood waste is attained. This is not possible in a wet process such as ordinarily found in a pulping process in which the reactor is charged with approximately 90% water which takes up space as well as requires the addition of large amounts of energy to bring the reaction medium to the proper temperature.

Another advantage is the contacting of lignocellulose or dry mixes of lignocellulose and other ingredients under superatmospheric pressure with a vapor or combination of vapors functioning both as a heat transfer medium and as a reactant.

In the method of this invention an essentially dry mixture including comminuted lignocellulose and a reactant including a base is reacted as by heating while confining the lignocellulose and the reactant under superatmospheric pressure as in an autoclave. During the reaction the lignocellulose bond is apparently broken and the lignin is released to operate as a binder.

It appears that the hemicelluloses are the primary constituents of the lignocellulose which are attacked by hydrolysis, but that under the high pressure and temperature of this invention a portion of the hydrolysates are further converted to higher molecular weight materials which can function as plasticizers for the autoclave product when it is molded. At the same time a controlled degradation of the alpha cellulose is carried out to the extent that the desired degree of moisture stability is obtained in the molded or extruded products without an unnecessary loss of toughness. These actions are believed to occur although they have not been absolutely proven.

The methods of this invention may be carried out batchwise in an autoclave or a sealed press or continuously in a continuous contactor.

The lignocellulose which appears dry to the touch actually contains up to about 30% water before the reaction begins.

The lignocellulose which may be used in this invention includes wood as well as other lignocellulosic vegetable materials. The lignocellulose is finely divided so that the particles are preferably not more than 20 mesh in size as measured by a standard screen although smaller sizes are preferred.

During the reaction which takes place in a confined atrnosphere under superatmospheric pressure various reaction products are produced although the exact nature of the reactions is not understood. It appears that the reaction products are either inert so that the product itself is inert, have a binding action such as is true of the lignin produced, are gaseous by-products, or are polymerized. By hydrolyzing and partially removing, or polymerizing the hemicelluloses to lignin type materials, the ratio of lignin and other binders to the alpha-cellulose is increased so that the general nature of the lignocellulose mixture is drastically changed.

The high pressure method of this invention has a number of advantages that are not possible with reactions taking place at ordinary pressures and in an unconfined state. In the preferred process, steam is introduced into the autoclave both for heating purposes and to supply moisture for the reaction. In the high pressure method of this invention heat transfer is much more rapid so that in general a shorter reaction time is required. Furthermore, energy losses during the reaction are greatly reduced. In the ordinary-reacting mixture these energy losses result from the release of volatile materials such as water vapor, gaseous reaction by-products and the like. As the reaction here takes place in a confined atmosphere, no such losses occur to any material degree. Furthermore, the energy supplied by the steam or vapor is utilized to heat only the lignocellulose with its ap proximately normal moisture content in contrast to pulping type reactions where large quantities of water are present, requiring far greater expenditures of energy.

Another important advantage of this process is the close control that is obtained over the reaction. Thus the temperature of the reacting mass, and hence the rate of reaction, can be easily raised or lowered by controlling the rate of flow, pressure and the temperature of the heat transfer medium which may be steam, oil vapor, or other high temperature fluids. Reactions may easily be stopped by flashing the heat transfer medium from the autoclave since the large energy losson expansion cools the reacting mass below the incipient reaction point. During the practice of the process the reacting mixture may be confined in a jacketed vessel with the heating medium introduced to the chambers in the quantity and temperature desired.

3 A very important advantage of the invention is that volatile reactants may be used as the reacting mass is in a confined space. Volatile reactants are impossible, of course, when the reacting mass is in the open. As a result of the rapid heat transfer achieved by this invention and the penetration of volatile reactants the reaction not' only proceeds to completion in a much shorter time but the final product tends to be more uniform than where the reactants are heated such as in an ordinary process that depends upon surface temperature difierentials.

Tests have shown that the confining of the reacting 7 for later use where desired or to prevent the creation of a nuisance.

Where volatile reactants are used in conjunction with the base no mechanical mixing of the ingredients is required. This results in a considerable saving in time, labor and other factors. Thus, in these instances, it is only necessary to charge the reactor with the lignocellulose and introduce the volatile materials into the reactor under superatrnospheric pressure. 'In addition, if desired, the reactants can be changed or modified during the course of a run. This is not possible to such a degree in a wet process where the charge generally contains less than 50% of lignocellulose, and addition of reactants would in many cases cause prohibitive amounts to go into solution.

A further advantage of utilizing a vapor process is that the volatile content of the reaction product which is primarily moisture can be controlled. By using superheated steam with a sufficient degree of superheat, products on the order of 1% or lower volatile content can be obtained. Under normal condition, 10 to 15 degrees of superheat at 300 pounds per square inch steam pressure will produce a product of 35% volatile content. Thus the expensive drying step connected with wet processes can be avoided.

Because of rapid penetration of reactants under high pressure, larger sized particles can be charged to the autoclave than would ordinarily be used, and a savings in size reduction cost made as a result of lower power requirements to reduce the treated material in comparison with raw lignocellulose.

In addition, where flat stock or preformed material'is being made as in a sealedpress, the products can be" made much thicker and more uniform than in an ordinary press which depends upon high platen temperatures for heat transfer, and in many cases requires almost prohibitive cycle times.

The preferred pressure in the reaction vessel during the reaction is preferably about 1004300 p.s.i. (pounds per square inch) gauge with about 300600 being especially preferred.

.The products of the reactions of this invention may be finished shapedmaterials or moldable compositions that may be used to make molded products. Where the prodnct is molded after the'reaction, this product is preferably removed from the reaction vessel and then ground to a 'fine powder that is preferably not over '50 mesh in size.'

The finely divided moldable material is heated to a temperature just sufiicient to cause the material to flow and fill the mold under the pressure used. This temperature is kept sufiiciently low, however, that losses are minor and breakdown due to decomposition'iskept to a minimum. The preferred temperature is between 250-450 F.

'The molding pressure may be any pressure suflicient I to cause the material to fill completely the mold and will vary depending upon the shape of the mold, the nature of the moldable material and other factors. In the preferred process to produce high density materials this pressure is between 2,00010,000 pounds per square inch. The molding time is only suflicient to cause the moldable material to fill the mold and set, and again will vary depending upon the type of mold being used, the temperature, the nature of the moldable material and similar factors. In general, the molding time will vary between 0.2-15 minutes. 7

The flow of the moldable material of this invention is improved and a shorter time is required if a plasticizer is added.

Plasticizers in general which have been found to be effective with the moldable materials include water; aromatic compounds containing a hydroxyl group such as aniline, phenol and cresol, alcohols such as benzyl, diethyleneglycol, glycerol, and furfnryl; nitrogen compounds such as formamide, urea, pyridine, and triethanolamine; and furfural.

The preferred plasticizers are water, furfural, aniline and phenol and the quantity utilized may vary depending on theflow desired. The preferred quantity is between about 2-20%.

In particular, the choice of plasticizer will depend upon the end use or method of fabrication of the material. The reaction products themselves are of a slow thermo setting nature. Thus, if a plasticizer such as water which is incapable of thermoset is used, the material is essentially of a thermoplastic nature. This is also true of the preferred plasticizers as a. group; however, when de sired, thermoset compositions can be made by using furfural, aniline or phenol in conjunction with a catalyst and, if desired, other materials capable of copolymerizatron.

Materials which will function as catalysts include the oxides, hydroxides and carbonates of the alkali and alkaline earth metals. The preferred catalysts are the oxides of magnesium and zinc.

Among the materials which may be used with the thermosetting plasticizers as copolymers are hexarnethylene tetramine, dimethylolurea, paraformaldehyde and urea.

Depending upon the set time required, about 05-50% of the catalyst and about 0.510.0% of the copolymer are used.

If desired, thermoset products can be obtained Without the use of catalysts or copolymers merely by heat treating the fabricated products after they have been molded or extruded.

If desired, pro-ducts of density ranging from 0.2l.3 specific gravity may be produced in the high pressure reacting vessel itself without requiring a subsequent molding operation as described above with high pressure molding. Here the finely divided lignocellulose and the reactant are mixed and the mixture cold pressed into the desired shape or compacted in a sealed press. The compressed mixture is then heated in the press or other high pressure vessel for the time required, at the required temperature and pressure. The material when removed from the reaction vessel will then be found to be quite hard and strong. In these instances, the reactant may be any of those set out above. 7

The preferred amount of base varies between about O.5-l5.0%, with an especial amount being about 0.5-5.07%,.by weight of the lignocellulose.

EXAMELE I To 500 grams of 20 mesh, hammer-milled ponderosa pine, containing only its normal moisture content of approximately 6.0%,'was added grams of a 5.0% aqueous solution of sodium'hydroxide. Based on the weight of the lignocellulose, the amount of solution was approximately 20.0%, and the sodium hydroxide was appr0ximately'1.0%. .The mixture was 'ball-milledfor one-half hour to obtain a uniform dispersion of the sodium hydroxide throughout the mass. T'nis composition was then placed in a heated autoclave, and steam was admitted until the pressure was 300 pounds per square inch gauge, and the temperature was approximately 440 F. The autoclave was held under these conditions for 20 minutes, and then the steam was rapidly flashed ofi. During the course of the run, the pressure was maintained at 300 p.s.i. by venting off the excess pressure caused by volatile reaction by-products. The granular reaction product, which had been cooled below the incipient reaction point by the rapid steam flash-off, was removed from the autoclave, and all particles which had consolidated were thoroughly broken up. The moisture or volatile content of this material was approximately 10.0%.

The following table sets forth a number of examples in which lignocellulose and sodium hydroxide were reacted by themselves, and in conjunction with other materials. The same procedures were followed as given above in Example I. Where finely divided solid additives such is lignin, Vinsol, phenolic residue, paraformaldehyde and sulfur are used with sodium hydroxide, they are preferably thoroughly blended with the lignocellulose in a ball-mill prior to the addition of the caustic solution. When liquids are used, they may be mixed separately with the lignocellulose or added as a single solution where they are mutually soluble.

Table I Percent Autoclave Sodium Example Hy- Additive droxide Time, Temp., PreSS Min. F. p.s.i

1.0 None 30 160 400 0.5 5% Ligniu. 25 4 10 300 1.0 ..do 25 440 300 1.0 do 40 440 300 2.0 .do 25 140 300 1.0 10% Lig'm'n 25 440 300 1. 5% Lignin 5% 25 440 300 BRV (Reclaim Oil). 9 1. 0 15% Vinsol 25 440 300 10 1. 0 10% Vinsol 3% 30 440 300 Paraiormaldehyde. 11 0 5% Phenolic Resi- 30 440 300 due 3% Paraformaldehyde. 12 1.0 do 40 440 300 13 1.0 10% Phenolic Resi- 30 440 300 due 3% Paraformaldehyde. 14 1. 0 6% Sulfur 25 440 300 15 2. 0 5% Cresol 5% Form 25 440 300 aldehyde 10% Paraflin Oil.

In the above table all percentages of additives are based on the weight of the lignocellulose. The preferred amount of sodium hydroxide used is between 0.5-10.0% based on the weight of the lignocellulose. Where Vinsol, lignin or phenolic residue are utilized they are preferably added in an amount equal to 2.030.0% of the weight of the lignocellulose.

Paraformaldehyde or formaldehyde are preferably used in an amount of between 2.020.0% of the weight of the lignocellulose, while cresol may be added in an amount of 2.0-25.0% by weight of the lignocellulose. Where oil such as paratfin or BRV are added they are preferably used in an amount of between 1.0-15.0% by weight of the lignocellulose.

Other alkalies and metal oxides have also been reacted with lignocellulose under the high pressure-temperature conditions of this invention. Among those are calcium hydroxide, magnesium hydroxide, and the oxides of zinc, iron, aluminum, titanium, manganese and boron. When such oxides, and hydroxides, which are sparingly soluble, are used, they are preferably added as finely divided solids, and thoroughly blended with the lignocellulose in a mixing device. A number of examples of reactions between lignocellulose and such alkalies and metallic oxides are set forth in the following table.

Table II Ex- Oxide Additive Time, Temp, Press ample Min. F. p.s.i

16.-- 0.5% Calcium"-.- None 20 140 300 17 3.0% Calcium "do 30 440 300 18 9.0% Calcium do 30 440 300 19 2.0% Galcium.- do 30 460 400 20.--" 5 0% Calciuun- 10% Sulfur 20 440 300 21- 2.0% Calcium--. 12% Sulfur 20 440 300 15% Vin sol 5% Aniline 22 do 5% C1'es01 30 460 400 23. 1.0% Magnesinm None 30 460 400 24. 5.0% Magnesium 25 440 300 25. 3.0% Zinc. 25 440 300 26. 30 460 400 27. 2 0% Aluminum. 15 460 400 28 1 0% Aluminum 30 460 400 29--- 1 0% Iron 30 460 400 30.--" l 0% Titanium 30 460 400 31"-.. 1.0% Manganese. 30 460 400 32"--- 1.0% Boron 30 460 400 Where the oxides or hydroxides listed in the above table are reacted with lignocellulose, they are preferably used in an amount of 0.5-15.0% of the weight of the lignocellulose. An especially preferred range is between 0.5-5.0% based on the lignocellulose.

In general, where alkalies are used, the reaction products can be utilized to make preforms, boards or moldings which are stronger than when plain lignocellulose is reacted with steam at high pressures. The alkalies and oxides appear to function as buffers during the hydrolytic reaction of the lignocellulose, thereby preventing excessive degradation of the alpha cellulose, so that boards made with such reaction products are stronger and tougher. This action is believed to occur, although it has not been absolutely proven.

'Ihe plenolic residue used herein is essentially a condensation product of phenol with acetone and alphamethyl styrene.

Vinsol is identified in my co-pending application Serial No. 608,196, filed September 6, 1956, now Patent 2,872,330.

Having described my invention as related to the embodiments set out herein, it is my intention that the invention be not limited by any of the details of description unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

I claim:

1. The method of making a lignocellulose product, consisting essentially of: intimately mixing particles of essentially dry lignocellulose with about 0.5 1511% of a metal oxide by weight of the lignocellulose; and heating the resulting composition in the presence of steam under super-atmospheric confined pressure of between about -600 pounds per square inch for between about 4-60 minutes and at between about 300-550 F. to form a reaction product of said metal oxide with the lignocellulose.

2. The method of making a lignocellulose product, consisting essentially of: intimately mixing particles of essentially dry lignocellulose with about 0.5l5.0% of a base of the class consisting of alkali metal and alkaline earth metal oxides, hydroxides and carbonates by weight of the lignocellulose; and heating the resulting composition in the presence of steam under superatmospheric confined pressure of between about 100-600 pounds per square inch for between about 4-60 minutes and at between about 300-5S0 F. to form a reaction product of said base with the lignocellulose.

3. The method of making a lignocellulose product, consisting essentially of: intimately mixing particles of essentially dry lignocellulose with about 0.515.0% of a magnesium oxide by weight of the lignocellulose; and heating the resulting composition in the presence of steam under superatmospheric confined pressure of between V lignocellulose.

minutes and at betweenxabot 300-5507 F.'to form a reaction product of said Zinc oxide with the lignocellulose.

References Cited file of this patent UNITED STATES PATENTS 1 2,440,789 Vander Pyl May 3, 1948 FOREIGN PATENTS Y 289,676 Great Britain May 3, 1928 497,477 Great Britain Dec. 16, 1938 

2. THE METHOD OF MAKING A LIGNOCELLULOSE PRODUCT CONSISTING ESSENTIALLY OF: INTIMATELY MIXING PARTICLES OF ESSENTIALLY DRY LIGNOCELLULOSE WITH ABOUT 0.5-15.0% OF A BASE OF THE CLASS CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL OXIDES, HYDROXIDES AND CARBONATES BY WEIGHT OF THE LIGNOCELLULOSE, AND HEATING THE RESULTING COMPOSITION IN THE PRESENCE OF STEAM UNDER SUPERATMOSPHERIC CONFINED PRESSURE OF BETWEEN ABOUT 100-600 POUNDS PER SQUARE INCH FOR BETWEEN ABOUT 4-60 MINUTES AND AT BETWEEN ABOUT 300-550*F. TO FORM A REACTION PRODUCT OF SAID BASE WITH THE LIGNOCELLULOSE. 